iPhone cannot reach Home Assistant

I’ve been running Home Assistant on a Raspberry Pi 4 for a few months. I had set up the companion app on my wife’s iPhone at the time, and everything was working well.

This morning I tried to set up the homekit integration and it timed out trying to connect to home assistant. I tried the app, but I just got a white screen (it’s using the ‘external’ IP, but that’s just 192.168.X.X:8123 on my network). Next up, I tried to access the install from a browser on the phone and still got a timeout. I can reach the router admin page from the phone browser, so it’s definitely able to access the local network. I can reach home assistant from a Mac browser, PC browser, android app on my phone, and also browser/app on a kindle fire.

I’m at a loss as to what might be causing the problem, preventing just the iPhone from reach HA. Even more perplexing, HA is able to send notifications to the companion app on the iPhone. What am I missing?